The present invention pertains in general to methods and apparatus for distributing fluids within a subterranean wellbore and in particular to methods and apparatus for distributing scale- or corrosion-inhibiting substances within a wellbore.
Deposition of scale on and corrosion of production equipment within a wellbore are severe problems in a number of oil fields. In some areas, corrosion problems are so great that downhole equipment must be pulled every few weeks for the purpose of replacement of damaged components. Scale buildup may be so severe that downhole submersible pump assemblies become insulated from the production fluid, causing the motor to heat up and fail prematurely. In other instances, scale buildup may be so severe that downhole components become stuck in the hole, so that their removal requires a costly fishing job.
One method of treatment for protecting well components involves continuously flushing scale and corrosion inhibitors down the annulus between production tubing and the well casing. Another protection method involves introducing a packer between the casing and the tubing above the production zone. Above the production zone, the tubing-casing annulus is filled with corrosion-and scale-inhibiting liquid. Neither of these techniques protects the casing or elements of the production tubing string below the point at which wellbore fluids are withdrawn into the production tubing.
Scale and corrosion below the production tubing intake is especially troublesome in deep wells where a downhole submersible pump is used to move production fluids towards the surface. Conventional methods of continuous flushing of scale and corrosion inhibitors or employing a packed-off, scale and corrosion inhibitor-filled annulus offer no protection to the seal and motor commonly found below the pump intake. Thus, frequent pulling of the well may be necessitated at great cost despite the use of scale and corrosion inhibitors.
One approach to scale and corrosion protection below the pump intake involves pumping scale and corrosion inhibitors from the surface down 3/4 inch coiled mild steel tubing which follows the production string and which attaches to a fiberglass tailpipe extending from the lower surface of a motor at the end of the production string to below the bottom of the production zone. This technique is successful in protecting downhole components, but is cumbersome, may require field-welding of lengths of tubing, and the tubing itself is subject to corrosion problems.